Method of forming a parabolic antenna

ABSTRACT

A method for forming a parabolic antenna almost entirely with plastic materials.

United States Patent MacTurk 1 July 29, 1975 METHOD OF FORMING A PARABOLIC ANTENNA [56] References Cited [75] Inventor: William L. MacTurk, Claremont, TED TATES PATENTS Calif. 2,742,387 4/1956 Givliani 29/600 3,024,525 3 1962 W' b 1 343 912 [73] Asslgneez General Dynamics Corporation, 3,030,259 411962 I I 154245 Pomona Callf- 3,169,311 2/1965 Small ct a1... 29/600 [22] Filed: May 6 1974 3,574,258 4/1971 May ct a1 29/600 [21] PP N04 467,034 Primary Examiner Caleb Weston Attorney, Agent, or Firm-Albert .1. Miller; Edward B. 52 us. c1. 156/245; 29/600; 29/601; Johnson 156/285; 156/289; 264/328; 343/912 [51] Int. Cl. H011 11/00 [57] ABSTRACT Field of Search 156/77 78, 2451 A method for forming a parabolic antenna almost entirely with plastic materials.

17 Claims, 16 Drawing Figures SI'iEET PATENTED JUL 2 9 I975 PATENTH] JUL 2 9 I975 SHEET PATENTEI] JUL29 I975 SHEET l/l/ll FIG.

FIG. l6

FIG. l4

METHOD OF FORMING A PARABOLIC ANTENNA BACKGROUND OF THE INVENTION The increased reliance of multi-band, broad band,

and higher frequency devices has introduced a command for cost reduction and lighter weight components with greater production simplicity.

One such component subject to these diverse demands is a microwave parabolic seeker antenna. This antenna, which may operate in the Ka-band with Cassegrainian feed, consists of a feed horn antenna incorporated into the center of a parabolic reflector by supports so that energy collected by the parabola is picked up by the scanning center of the hyperbolic reflector and focused into the horn antenna and then fed through a section of waveguide.

While prior art production methods, exemplified in US. Pat. Nos. 2,689,304, 2,742,387, 3,167,776, 3,169,311, 3,187,064, 3,381,371, 3,383,152 and 3,390,214 can be utilized to produce a microwave parabolic seeker antenna, there is a pressing need for a lower cost, lighter weight antenna having improved reliability and batch production capability.

SUMMARY OF THE INVENTION The invention is directed to a method of forming a parabolic antenna almost entirely with plastic materials. The techniques of injection molding, vacuum forming, pressure forming, foaming, and chemical plating are integrated into an overall process around a basic set of tooling which is utilized repeatedly throughout the process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is a perspective view of the tooling for holding the parabola blank.

FIG. 5 is a sectional view of the concave epoxy paraboloid, the parabola blank holding tooling, and the basic tooling assembled in a press.

FIG. 6 is a perspective view of the parabola formed by the assembled tooling of FIG. 5.

FIG. 7 is an exploded view of the tooling for forming the plastic mounting plate.

FIG. 8 is a sectional view of the assembled tooling of FIG. 7.

FIG. 9 is a perspective view of the mounting plate formed in the tooling of FIGS. 7 and 8.

FIG. 10 is a sectional view of the tooling for forming the plastic collar.

FIG. 11 is a perspective view of the plastic collar formed in the tooling of FIG. 10.

FIG. 12 is a perspective view of the plastic collar of FIG. 11 assembled with the mounting plate of FIG. 9. 65

FIG. 14 is a perspective rear view of the parabola assembly formed in the tooling of FIG. 13.

FIG. 15 is an exploded view of a parabolic antenna including the parabola assembly formed in the assembly of FIG. 13.

FIG. 16 is a perspective view of an assembled parabolic antenna produced in accordance with the method of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Some of the basic tooling for the manufacturing method of the present invention is illustrated in FIGS. 1 and 2. This tooling, shown in an exploded view in FIG. 1, comprises a hollow cylindrical mold ring 10, a flat circular cover plate 12, and a convex paraboloid circular plate 14. The mold ring 10, cover plate 12 and convex paraboloid plate 14 may all be machined from aluminum. A tape-controlled lathe can be utilized to produce the convex paraboloid surface 15 on plate 14 to the surface of revolution y= V 8x where y defines the length along the radius of the circular parabola from the point of origin and x defines the depth of the parabola at point y.

In order to assemble the mold ring 10, cover plate 12 and convex paraboloid plate 14 into the mold assembly 16 of FIG. 2, a plurality of holes 18 are drilled and tapped through the mold ring 10, with aligned holes 20 drilled through the cover plate 10 around the periphery thereof. The holes 18 are threaded on each side to accept right hand threads. Around the periphery of the convex paraboloid plate 14, a plurality of holes 22 are drilled through. The cover plate 12 additionally includes a plurality of holes 24 drilled through the plate in the central portion thereof and including a central hole 25.

Before the mold assembly 16 is formed, the interior mold surfaces of the mold ring 10, cover plate 12 and convex paraboloid plate 14 are highly polished and then waxed. The mold ring 10 is then placed over the convex paraboloid plate 14 with the threaded mold ring holes 18 aligned with the peripheral holes 22 of the convex paraboloid plate 14 and then fastened together with a plurality of threaded bolts or screws 23 which extend through the holes 22 into the threaded holes 18.

A room temperataure curing plastic, such as stycast epoxy, is poured into the mold ring 10 over the convex paraboloid plate 14 to completely fill the mold ring 10. The cover plate 12 is then placed over the filled mold ring 10 and the mold assembly 16 is fastened together with a plurality of threaded bolts or screws which extend through the cover plate 12 and into the tapped holes of mold ring 10. Any excess epoxy can ooze out of the mold assembly 16 through the holes 24 and 25 in the cover plate 12.

After the epoxy is cured in the mold assembly 16 for 24 hours at room temperature, the cover plate 12 and convex paraboloid 14 are removed from the mold ring 10. The concave epoxy paraboloid 28 formed in the mold ring 10 does not adhere to the waxed interior surfaces of the plates 12 and 14. This concave epoxy paraboloid 28 in the mold ring 10 is shown more clearly in FIG. 3 and is ready to be used in later steps in the fabrication process.

The next step in the method is to assemble the parabolic reflector blank holding tool 30 shown in FIG. 4. The reflector blank 32, which is a flat copper or copper plastic sheet, such as mil thick polyethylene plastic coated on both sides with 1 02. copper or mil thick polyolefin plastic with 1 mil thick highly polished copper on both sides, is held between a holding tool upper ring 34 and a holding tool lower ring 36. The upper and lower rings 34 and 36, of a material such as aluminum, are held together by a plurality of screws 38 which also extend through guide posts 40 extending upward from the upper ring 34.

As shown in FIG. 5, the assembled holding tool is placed over the concave paraboloid 28 in the mold ring 10. The lower ring 36 fits over the mold ring 10 such that the periphery of the blank 32 rests on the top of the mold ring 10. The convex paraboloid plate 14 is then placed over the holding tool 30 with the convex paraboloid surface 15 towards the parabolic reflector blank 32. The guide posts center the convex paraboloid plate 14 over the blank 32.

The above assembly is then placed into a press having a base 42 and ram 44. The blank 32 is then pressure formed into the parabolic reflector 46 of FIG. 6 by the exertion of a nominal press force, between 50 and 500 lbs. With the assembly removed from the press, the convex paraboloid plate 14 and the holding tool 30 can be removed and a plurality of holes 46 drilled in the rim 50 of the parabolic reflector 46 alinged with the holes 18 in the mold ring 10.

The thus formed parabolic reflector 46, which can be gold plated if desired, has a coordinate surface within 0.002 inches of the convex paraboloid surface of plate 14. Little or no springback has been evidenced upon removal from the tool. Protection from dust, foreign particles, and contamination was also afforded during forming.

The injection mold tooling of FIGS. 7 and 8 is used to form the mounting plate 52 of FIG. 9. The mold 54 is assembled to a cover plate 13 by means of pins 56 extending from the mold 54 through holes 21 in the cover plate 13 to form a mold cavity 60 in which the mounting plate 52 is formed. Threaded metal inserts 62 are inserted into the mold cavity 60 through the holes 27 in the cover plate 13. A rectangular insert 64 is also inserted into the cavity 60 at the center thereof. A fill hole 29 is drilled through the cover plate 13.

With the mold tooling assembled as shown in FIG. 8, the mounting plate 52 is formed by injecting high density ABS (Acrylonitrile Butadiene Styrene) plastic into the mold cavity 60 via the fill hole 29. An injection molding temperature of 375F with a mold pressure of 9750 psig will produce satisfactory results.

As illustrated in FIG. 9 the threaded metal inserts 62 are molded in place into the mounting plate 52. These inserts 62 can later be used to attach RF elements to the mounting plate 52. The rectangular insert 64, when removed from the mounting plate 52, leaves a rectangular slot 66 in the mounting plate 52 which can later be used to hold the base of a waveguide feed born.

The mold ring 10 is placed around a circular base plate 31 and is then utilized to form a plastic collar 68 as shown in FIG. 10. A l/l6 inch thick white ABS plastic is vacuum formed (pulled down) over the ring 10 utilizing standard vacuum forming techniques. Any excess plastic on the outside of the mold ring 10 is removed and the collar rim 70 trimmed. Holes 72 aligned with the holes 18 in the mold ring 10 are drilled in the collar rim 70. The central portion of the collar base 74 is then cut out as illustrated in FIG. 11. The mounting plate 52 of FIG. 9 and the plastic collar 68 are then bonded together with a resin adhesive as shown in FIG. 12.

The parabolic antenna 76 of FIG. 15 is produced in the assembled tooling of FIG. 13. The copper-plastic parabolic reflector 46 of FIG. 6 is placed over the convex paraboloid plate 14 with the rim holes of parabolic reflector 46 aligned with the plate holes 22. The plastic collar 68 and mounting plate 52 in mold ring 10 are then placed over the parabolic reflector 46 and plate 14 with the collar rim holes 72 and ring mold holes 18 aligned with holes 48 and 22 in the parabolic reflector 46 and plate 14 respectively.

The prescribed quantity of 2-lb polyurethane foam is then inserted into the cavity 78. The cover plate 12, with holes 22 aligned with the holes 72, 18, 48 and 22, is then placed over the mold ring 10 and bolted into place. Venting of any gases is accomplished through the feed horn slot 66 in the mounting plate 52 and the central hole 25 in the cover plate 12. Screws 80 may be inserted into the threaded inserts 62 in the mounting plate 52 through holes 24 in the cover plate 12 to prevent any polyurethane foam from filling the inserts 62.

The entire assembly of FIG. 13 is then placed in an oven to cure the polyurethane foam. A convection oven at 160F for 2 hours has been found to be satisfactory. On removal from the oven and cooling to room temperature, the unit is disassembled. The parabola rim 50 and plastic collar rim 70 are then trimmed to produce the parabolic antenna 76 shown in FIG. 14 (rear view) and in FIG. 15 (front view). By this technique, no wax is required to prevent adhesion of the polyurethane foam to any metal surface of the mold since the mold is completely protected by the plastic configuration and is an integral assembly. After curing an extremely strong, rigid, lightweight parabolic antenna 76 is thus produced in which the parabolic reflector 46 is fully supported.

In order to make a complete parabolic antenna assembly as shown in FIG. 16, four equidistant holes 84 are drilled into the reflective surface 86 of the parabola assembly 76, as illustrated in FIG. 15. A rectangular slot 88 is also machined through the parabolic antenna 22 in alignment with the slot 66 in the mounting plate As illustrated in FIG. 15, a plastic waveguide feed horn 90 is press fitted into the slot 88 in the parabolic antenna 76. A threaded plastic hyperbola 92, having a copper plated hyperbolic surface 94, is screwed into a plastic mounting structure 96 having four legs 98 which are press fitted into the four holes 84 in the reflective surface 86 of the parabolic antenna 76. The legs 98 support a threaded hollow tube 100 in which the hyperbola 92 is threadally disposed. A notch 102 is provided at one end of the hyperbola 92 to facilitate adjustment thereof in the threaded hollow tube 100. The complete functional parabolic antenna assembly is shown in FIG. 16.

In the above manner, a complete parabolic antenna can be produced from plastic materials with great ease of manufacture and with considerable savings in cost and weight over conventional structures. In addition, a truly functional design is produced with increased reliability.

While specific embodiments of the invention have been illustrated and described, it is to be understood that these are provided by way of example only and that the scope of the invention is to be determined by the proper scope of the appended claims.

What I claim is:

1. A method of forming a parabolic antenna comprising the steps of:

molding a concave epoxy paraboloid mold;

disposing a parabolic reflector blank over the concave epoxy paraboloid mold;

pressure forming the parabolic reflector blank into the concave epoxy paraboloid mold to form a parabolic reflector;

molding an antenna mounting plate;

forming a plastic collar for the parabolic reflector;

bonding the antenna mounting plate to the plastic collar;

assembling the parabolic reflector together with the plastic collar and mounting plate; and

inserting a plastic material between the parabolic reflector and the bonded plastic collar and mounting plate.

2. The method of claim 1 and including the steps of mounting a plastic waveguide feed horn and a plastic hyperbola on the parabolic antenna.

3. A method of forming a parabolic antenna comprising the steps of:

forming a mold to mold a concave epoxy paraboloid,

said mold comprising a hollow cylindrical mold ring disposed between a plate having a convex paraboloid surface and a first flat cover plate; molding a concave epoxy paraboloid in the mold; disposing a parabolic reflector blank between the convex paraboloid surface plate and the concave epoxy paraboloid; pressure forming a parabolic reflector from the parabolic reflector blank disposed between the convex paraboloid plate and the concave epoxy paraboloid;

forming a mounting plate injection mold with a second flat cover plate and a mold plate;

injection molding an antenna mounting plate in the mounting plate injection mold;

vacuum forming a plastic antenna collar around the hollow cylindrical mold ring;

bonding the antenna mounting plate to the antenna plastic collar;

assembling the parabolic reflector and the bonded antenna plastic collar and mounting plate within the cylindrical mold ring between the convex paraboloid plate and the flat cover plate; and

inserting a plastic material between the parabolic reflector and the bonded antenna plastic collar and antenna mounting plate.

4. The method of claim 3 and including the steps of mounting a plastic waveguide feed horn and a plastic hyperbola on the parabolic antenna.

5. The method of claim 3 wherein said mold ring, said convex paraboloid plate and said first fiat cover plate are formed from aluminum.

6. The method of claim 5 wherein the convex paraboloid mold surfaces are polished and waxed before the concave epoxy paraboloid is molded.

7. The method of claim 6 where said concave epoxy paraboloid is molded from a room temperature curing epoxy.

8. The method of claim 7 wherein said concave epoxy paraboloid is molded from stycast epoxy.

9. The method of claim 8 wherein said stycast concave epoxy paraboloid is cured for 24 hours.

10. The method of claim 3 wherein said parabolic reflector blank is held between two holding rings.

11. The method of claim 10 wherein said parabolic reflector blank is a thin copper sheet.

12. The method of claim 10 wherein said parabolic reflector blank is a polyethylene plastic sheet coated on both sides with copper.

13. The method of claim 10 wherein said parabolic reflector blank is a polyolefin plastic sheet coated with polished copper on both sides.

14. The method of claim 10 wherein said pressure formed parabolic reflector is gold-plated.

15. The method of claim 3 wherein said antenna mounting plate is molded of high density ABS plastic.

16. The method of claim 3 wherein said antenna plastic collar is vacuum formed of white ABS plastic.

17. The method of claim 3 wherein the plastic material used in the last step is polyurethane which is then oven cured at lF for 2 hours. 

1. A METHOD OF FORMING A PARABOLIC ANTENNA COMPRISING THE STEPS OF: MOLDING A CONCAVE EPOXY PARABOLOID MOLD DISPOSING A PARABOLIC REFLECTOR BLANK OVER THE CONCAVE EPOXY PARABOLOID MOLD PRESSURE FORMING THE PARABOLIC REFLECTOR BLANK INTO THE CONCAVE EPOXY PARABOLIOD MOLD TO FORM A PARABOLIC REFLECTOR, MOLDING AN ANTENNA MOUNTING PLATE, FORMING A PLASTIC COLLAR FOR THE PARABOLIC REFLECTOR, BONDING THE ANTENNA MOUNTING PLATE TO THE PLASTIC COLLAR, ASSEMBLING REFLECTOR TOGETHER WITH THE PLASTIC COLLAR MOUNTING PLATE, AND
 2. The method of claim 1 and including the steps of mounting a plastic waveguide feed horn and a plastic hyperbola on the parabolic antenna.
 3. A method of forming a parabolic antenna comprising the steps of: forming a mold to mold a concave epoxy paraboloid, said mold comprising a hollow cylindrical mold ring disposed between a plate having a convex paraboloid surface and a first flat cover plate; molding a concave epoxy paraboloid in the mold; disposing a parabolic reflector blank between the convex paraboloid surface plate and the concave epoxy paraboloid; pressure forming a parabolic reflector from the parabolic reflector blank disposed between the convex paraboloid plate and the concave epoxy paraboloid; forming a mounting plate injection mold with a second flat cover plate and a mold plate; injection molding an antenna mounting plate in the mounting plate injection mold; vacuum forming a plastic antenna collar around the hollow cylindrical mold ring; bonding the antenna mounting plate to the antenna plastic collar; assembling the parabolic reflectoR and the bonded antenna plastic collar and mounting plate within the cylindrical mold ring between the convex paraboloid plate and the flat cover plate; and inserting a plastic material between the parabolic reflector and the bonded antenna plastic collar and antenna mounting plate.
 4. The method of claim 3 and including the steps of mounting a plastic waveguide feed horn and a plastic hyperbola on the parabolic antenna.
 5. The method of claim 3 wherein said mold ring, said convex paraboloid plate and said first flat cover plate are formed from aluminum.
 6. The method of claim 5 wherein the convex paraboloid mold surfaces are polished and waxed before the concave epoxy paraboloid is molded.
 7. The method of claim 6 where said concave epoxy paraboloid is molded from a room temperature curing epoxy.
 8. The method of claim 7 wherein said concave epoxy paraboloid is molded from stycast epoxy.
 9. The method of claim 8 wherein said stycast concave epoxy paraboloid is cured for 24 hours.
 10. The method of claim 3 wherein said parabolic reflector blank is held between two holding rings.
 11. The method of claim 10 wherein said parabolic reflector blank is a thin copper sheet.
 12. The method of claim 10 wherein said parabolic reflector blank is a polyethylene plastic sheet coated on both sides with copper.
 13. The method of claim 10 wherein said parabolic reflector blank is a polyolefin plastic sheet coated with polished copper on both sides.
 14. The method of claim 10 wherein said pressure formed parabolic reflector is gold-plated.
 15. The method of claim 3 wherein said antenna mounting plate is molded of high density ABS plastic.
 16. The method of claim 3 wherein said antenna plastic collar is vacuum formed of white ABS plastic.
 17. The method of claim 3 wherein the plastic material used in the last step is polyurethane which is then oven cured at 160*F for 2 hours. 